Crystal heterophase crystallization

In rubber-plastic blends, clay reportedly disrupted the ordered crystallization of isotactic polypropylene (iPP) and had a key role in shaping the distribution of iPP and ethylene propylene rubber (EPR) phases larger filler contents brought about smaller, less coalesced and more homogeneous rubber domains [22]. Clays, by virtue of their selective residence in the continuous phase and not in the rubber domains, exhibited a significant effect on mechanical properties by controlling the size of rubber domains in the heterophasic matrix. This resulted in nanocomposites with increased stiffness, impact strength, and thermal stability. 

In Section 9.4.1, we introduced internal electrochemical reactions by considering heterophase AX/AY assemblages. We now discuss the more general case of internal electrochemical reactions which occur in inhomogeneous systems having various types of disorder. From the foregoing discussion, we expect internal reactions to occur in a crystal matrix whenever the condition V/jon = 0 is not met. The extreme is a transition from n- (or p-) type conduction to ionic conduction (which for brevity we shall call a (n-i) junction). 

Interfaces may also be classified broadly into homophase interfaces and heterophase interfaces. A homophase interface separates two regions of the same phase, whereas a heterophase interface separates two dissimilar phases. Crystal/vapor and crys-tal/liquid interfaces are heterophase interfaces. Crystal/crystal interfaces can be either homophase or heterophase. Examples of crystal/crystal homophase interfaces are illustrated in Figs. B.2, B.4, and B.5. Examples of heterophase crystal/crystal interfaces are shown in Figs. B.6 and B.7. Figure B.6o shows an interface between f.c.c. and h.c.p. crystals where the small mismatch between close-packed lll fcc... 

Figure B.7 Construction of a heterophase interface, (a) Reference crystal taken to be...

All sharp crystal/crystal homophase and heterophase interfaces can be classified as coherent, semicoherent, and incoherent. The structural features of these interfaces can be revealed by constructing them using a series of operations which always starts with a reference structure. 

Thus, melting of a crystalline substance without superheating is a superficial effect. Pre-melting phenomena are apparently also related to the formation of liquid films on the surfaces of crystals, if not to other incidental causes (for example, impurities), and are not pertinent to Frenkel s theory. Heterophase fluctuations are quite large where the difference between two phases and the surface tension between them tend to zero—near the critical point and near the Curie point. The first case is commonly known, the second was earlier investigated quantitatively in Landau s fine work [13, 14]. 

An extension of the kinetic theory on cases when a mechanical pressure interacts with kinetic processes inside solid volume and on interfaces has wide application interests. The elastic deformations in solid are presented from influence of external forces and from presence of internal defects of crystal structure point defects (vacancy, intersite atoms, complexes of atoms, etc.), extended defects (dislocations and inner interfaces in polycrystals), and three-dimensional defects (heterophases crystals, polycrystals). 

The ordering may also occur in liquid states especially in those which are able to form liquid crystals. The lower the heat of the phase transition, the higher will be the probability of appearance of heterophasal fluctuations, whose existence has been proved directly for the acids studied (23). 

Silicate phases of granite. Most of natural materials are multicomponent heterophase mixtures of minerals, for example, granites are composed of the silicates of different structures. The main types of crystal structures in silicate phases of granite powder are framework, layered and chain-like structures built of Si04 tetrahedrons. 

Diffusion from the surface layer to the crystal bulk plays an important role in heterophase systems. It is the diffusion processes that determine in large part whether or not ZnO layers will grow and whether the ZnO/ZnSe(S,Te) heterojunction will have a sharp interface or the ZnO layer will grow via oxygen diffusion into the crystal bulk and will have a broad boundary. Solving Eqs. (8-11), one can determine, from the relationship between the generation rates of A and B vacancies, the quasi-heteroepitaxy parameters at which particular kinds of heterojunctions, conductivity types, and defect concentrations in ZnO and ZnSe(S, Te) layers can be obtained. 

Final comment. The spontaneous growth from fluxes does not always provide only the desired phase. In the case of heterophase growth a first selection of the crystals on the basis of some diagnostic properties is the best way to avoid an incorrect representation of the phase state in the polysulfide systems. 

First, the system has to be very anhydrous, thus a feed stock preparation is essential. Secondly, one must achieve a totally homogeneous reaction. The catalyst must be in solution or seeming so. The sugar must be totally in solution. All of the intermediate products and final products must remain in solution. If they do not, one runs into troubles with reactor problems. All reactors foam, spatter, mist and so forth. They have hot zones and cold zones, crystallization areas and charing areas. Maintaining beneficial color and avoiding by-products usually is very difficult if one must try to manipulate heterophase, suspension reactions. One demand is that there be no preperoxidation or oxidation of the methyl esters. However,... 

Keywords peroxide, molar weight distribution (MWD), rheology, crystallization, extrusion, melt flow index (MFI), controlled rheology (CR), peroxide-degradation, residence time distribution (RTD), halflifetime of peroxides, melt elasticity, die swell, viscosity curve, shear rate, elongational viscosity, melt fracture, heterophasic PR... 

Fig. 39. Micro-EDX analysis of Ndl23 crystals grown by the modified TSSG method in low-Po, atmosphere from contamination-firee Nd Oj crucibles with different post-growth heat treatments. In all the cases final oxygenation at 340°C in oxygen was applied. The picture demonstrates (a) tweed structure formation and (b) nanoscale composition fluctuations in crystals with the anomalous peak effect on a magnetization curve. Note that the composition profile for heavy atoms (Ba/Nd ratio) is similar to wave-like fluctuations typical for demixing behavior or a spinodal homophase decomposition rather than for a heterophase decomposition with the formation of a boundary between the crystal matrix and the precipitated phase (M. Nakamura et al. 1996c).

In this section we will investigate fluctuations that result in the formation of small spatial regions of the low temperature, liquid-crystal phase in the isotropic phase, as the temperature T approaches Tc from above. These so-called heterophase fluctuations produce a... 

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